Electronic devices, both consumer and commercial, are increasingly portable. One carries their telephone, PC, pager (to the extent anyone still has one), PDA, GPS decoder, and a myriad of other devices. Each of these devices requires a portable power source. For reasons of ease of use and economic efficiency, the power source of choice is a rechargeable battery.
Contact-less energy transfer can be used to eliminate the cost of a connector and associated reliability problems in providing power to recharge battery-operated portable electronic devices. Typically, existing contact-less battery charging methods use a two-stage solution. In the first stage of the system, located on a host charging circuit on an external device, a first controller or regulator is used to generate a voltage. This voltage, which is usually not very accurate, is then transferred to a secondary stage located on the portable device where the battery being charged is found. The second stage requires an additional controller or regulator to manage the current charging the battery. An example of such a two stage energy transfer system, is described in U.S. Pat. No. 6,301,128 B1. Although not directly addressing battery charging, the use of a two-stage system for energy transfer is well illustrated.
The use of such a two-stage power conversion system increases the costs of the charging system, increases the complexity and size of the portable device, and decreases the efficiency of the power conversion. Moreover, as stated above, the voltage coming off of the host first stage tends to be inaccurate. This is due to the fact that if there is no direct feedback from the secondary side, the primary side simply cannot have an accurate representation of the output voltage/current. In such circumstance the regulation is simply not as accurate, inasmuch as there is an attempt to control an output without accurately monitoring it. What is needed is an improved method of contact-less power conversion that obviates the cumbersome requirements of the prior art, increases accuracy in the generated charging voltage, and increases efficiency.